In order to fasten a plurality of members to be fastened, screw members such as bolts and nuts are often used, and in order to prevent the fastened screw members from becoming loose, a locking member such as a spring washer is normally used.
In order to prevent the screw members fastened to each other from becoming loose, without using such an additional part, there has been used a self-lock screw member as described in the Japanese Patent Publication No. 56-19492 and the Japanese Patent Publication No. 3-46686.
The self-lock screw member described in the Japanese Patent Publication No. 56-19492 is constructed such that a flank angle of a screw thread of a first screw member is set to be smaller than a flank angle of a screw thread of a second screw member meshed therewith, and in the thread of the first screw member, there is formed a slit radially extending from the point thereof. This screw member is formed such that when the first screw member and the second screw member are thread-connected, the thread of the first screw member elastically deforms in the direction that the slit becomes narrow, and due to a righting moment thereof, the self-lock function is exhibited.